Whitehaven Coal shares have fallen after the company posted a $47 million first half loss.

Lower coal prices and delays to operations prompted the fall from a $19.9 million profit in the previous corresponding period for the NSW-focused miner.

Whitehaven shares had fallen six cents, or two per cent, to $2.94 at 1155 AEDT.

"Whitehaven's first half performance has suffered from a number of adverse impacts on the business, the most significant being weak coal prices and a strong Australian dollar," outgoing chief executive Tony Haggarty said in a statement.

The company was also impacted by a train derailment and the closure of its Sunnyside mine.

Mr Haggarty, who leaves the company in March, said Whitehaven was reviewing its operations to identify ways of further reducing costs and improving revenue.

The value of Whitehaven's coal has also been negatively affected by a high moisture content in coal from its Narrabri mine, reducing its energy.

That coal has to be sold in lower-priced coal markets.

The high moisture content was expected to persist into the second half of the financial year, although an improvement was expected in the final three months, Whitehaven said on Tuesday.

The benchmark price of its Newcastle semi-soft coking coal had remained stable at around $US113.50 per tonne in the three months to December, and that was expected to continue in the three months to the end of March, the company said.

About 1.4 million tonnes of coal were expected to be sold to existing customers over the year, the company said, adding that winning new business at reasonable prices was difficult.

The company upgraded its total coal resources by two per cent to 3.788 billion tonnes.